I wouldn’t bother buying separate personally! We have always just used whatever we have
Morrisons unsalted butter.
Just use whatever you have. You shouldn’t be absolutely capping it anyway so they won’t get much of the ‘bad stuff’
We just use whatever we have! We only put a thin layer on anyway so thought it couldnt hurt, we currently have i cant believe its not butter but usually get flora if its on offer
I normally get Tescos own brand unsalted butter and keep it in a butter dish. We have it open a while but has never gone bad.